1. Field of the Invention
This invention relates to scroll-type fluid machinery functioning as compressors, expanders or vacuum pumps, and more particularly to twin unit scroll-type fluid machinery having stationary scrolls axially disposed on both sides of an orbiting scroll.
2. Description of the Prior Art
Scroll-type compressors which are known in the art comprise: a stationary scroll having a first wrap formed in an involute spiral located within a casing which encloses all members thereof, a peripheral wall provided with a suction port and an exhaust port at a peripheral region and a central region thereof, respectively, an orbiting scroll having a second wrap also formed in an involute spiral, the second wrap mating with the first wrap at least in a pair of line contacts thereby forming a pocket between the line contacts of the first and second wraps, wherein, when the orbiting scroll is driven with an orbital movement rather than a rotational movement, air is taken through the suction port into the pocket whose volume is reduced as it moves along the scroll surfaces to the central region, the compressed air being discharged through the exhaust port. There is disclosed in U.S. Pat. No. 4,129,405 single unit scroll-type machinery for expanding, compressing or displacing fluid with a stationary scroll and an orbiting scroll interfitted to each other. U.S. Pat. No. 4,192,152, and Japanese Patent Publication 63-42081 disclose twin unit scroll-type machinery for expanding, compressing or displacing fluid with a pair of stationary scrolls, each having a wrap inside, and with an orbiting scroll having wraps on both sides which are interfitted respectively with the mating wraps of the stationary scrolls.
In either of the scroll-type machineries above, however, problems arise at the suction port and the exhaust port, because each of the wraps of the stationary scroll and the orbiting scroll is formed with the same number of turns, the wraps being engaged with a 180 degree phase difference.
That is, in the region of the suction port, there has to be provided another suction port 180 degrees apart from the first suction port, where each beginning end of the wraps contacts the other wrap side walls and forms one of the contact lines of the pockets, or there has to be provided a half-way detour passage circumferentially around the periphery of the wraps which connects the suction port with the other side of the contact line 180 degrees apart therefrom. These problems result in machinery that is large in size and sophisticated in machining and assembling processes.
The two suction ports, further, means there are two pockets 180 degrees apart which are hard to simultaneously compress, thereby requiring double power, and reducing the intake efficiency because the fluid volume sucked in the pockets is limited by the port area and the detour passage.
The problem in the region of the exhaust port, on the other hand, resides in the large volume of the pockets at the central portion, where an eccentric shaft has to be provided axially parallel with a drive shaft to drive the orbiting scroll together with a bearing thereof, where the exhaust port and a terminal wrap end have to be provided at the peripheral circumference of the bearing, and where the involute spiral terminates before reaching the center thereof, without shortening the spiral's length in order to obtain smaller pocket volume because there has to be disposed a pair of terminal wrap ends 180 degrees apart. Thus, conventional machineries result in the pocket volume released at the exhaust port remaining so large as not to attain a maximum compression ratio. What is worse, the greater volume of the pocket at the last stage makes the sealing line longer, making leakage easier, and the resulting compression efficiency lower.
To solve these failures, in a single unit scroll-type machine, an arrangement may be provided wherein a main shaft to drive an orbiting scroll is disposed at the back surface thereof, and an exhaust port is provided at the center of a stationary scroll. Whereas, in the twin unit scroll-type machine as shown later in the embodiment of the present invention, the main shaft to drive the orbiting scroll has to be disposed through the stationary scrolls at the center thereof, because the orbiting scroll has to be oppositely interfitted with the stationary scrolls so as to arrange a pair of stationary scrolls at both sides of the orbiting scroll, wherein it is necessary that the exhaust port and the terminal wrap ends have to be disposed at the peripheral circumference of the bearing where the involute spiral terminates before reaching the center thereof.
In either scroll-type machine, because the wrap ends slide on the opposite mirror surface, lubricated with grease, in substantial surface contact in order to compress the fluid, the scrolls opposing each other have to be aligned parallelly and axially within a strict limitation.
A plurality of thrust adjusting means are provided to solve the problem in either scroll-type machine. At the peripheral wall of the stationary scroll opposite to the orbiting scroll, which wall is located outside of the wrap space where the compression is effected, three sets of slave crank shafts are provided in a 120 degree distribution, for example, whereby the parallel alignment of the scrolls and the thrust adjustment is effected.
Because the twin unit scroll-type machine above, however, is formed whereby the orbiting scroll is interfitted with a pair of stationary scrolls at either side, the thrust adjusting means must be provided at each of the stationary scrolls in order to adjust the thrust through the orbiting scroll commonly held at both sides thereof. Thus, if the thrust of one side of the stationary scroll is adjusted, then the thrust already adjusted on the other side of the stationary scroll becomes deviated.
Therefore, as in Japanese Patent Publication 63-42081, utilizing a main shaft which drives the orbital scroll disposed coaxially with a pair of stationary scrolls, and a plurality of eccentric shafts to restrict a rotational movement, the scrolls are intended to be precisely assembled in a unit with bearings, a casing and so forth, to avoid misalignment of the scrolls with each other, and misalignment of the thrust. The arrangement of the three scrolls with the main shaft and the eccentric shafts assembled in one unit with a plurality of parallel axes does not allow the orbiting scroll to have the slightest axial deviation. Even if the deviation may be allowed within some extent, another failure arises in that the tolerance may require further shaft power.
Though the twin unit scroll-type fluid machine has been believed to have a great advantage due to its small size, resulting from the compression procedure available at both sides of the orbiting scroll, and forming a two stage compressor with a higher compression ratio, hence, with a better power efficiency, the twin unit machine has not been completely successful because of the troublesome issues discussed above.